Broad application of fluid-logic systems to date has not been practicable because of the following limitations in existent hardware:
1. Available devices dissipate a relatively high percentage of their power in continuous bleed-off or exhaust; PA1 2. They operate at such low pressures that line losses become drastically significant: additional elements and connecting plumbing compel new circuit analysis and pressure-drop allowance. PA1 3. Again because of these low pressures (typically a few inches of water pressure), these devices are not normally capable of performing useful work and must be supplemented by separate output interface devices to develop enough power to get jobs done. PA1 4. Many industrial users have had difficulty in meeting the fluid-logic system requirement for clean, dry air that low-pressure, small-orifice devices demand--with the result that such systems would prematurely fail. PA1 5. Practically all the fluid-logic devices available to date have been digital (receiving and processing information in the form of discrete signals that are either "on" or "off"), because it is considered easier and less expensive to make such components. This factor has limited the use of fluid-logic in automatic control applications, because the latter usually involve continuous-variable analog inputs, such as voltage, resistance, position, etc. PA1 1. Analog-signal sensor-input termination point; PA1 2. Analog-to-digital signal-conversion interface; PA1 3. Control gate, during threshold mode; PA1 4. Interaction region wherein regenerative feedback initiates and proceeds; PA1 5. Differential force sensor--a logic-circuit element to decide when some command-signal or other predetermined input may be exceeded by the analog input signal, and to deliver such decision as an order to the control element; PA1 6. Control-element output device, to vary the flow of control-agent fluid in measure as the thus-established closed-loop feedback control circuitry may determine and dictate.
It has been noteworthy that in the field of electronics the development of the silicon controlled rectifier as the most important member of the thyristor family of devices, has greatly simplified switching problems and eliminated the need for separate arrays of output interface devices and coordinating logic devices. As the above limitations indicate, there has been a parallel need to develop a similar thyristor-like device for the field of fluid logic. The present invention is such a device: a high-gain, gate-controlled, bistable, fluid-logic switch. It is prospectively as important a building-block element in practical fluid-logic circuits as has been the silicon controlled rectifier in electronics.